JP5355381B2 - Imaging apparatus and focus control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To rapidly bring a subject to be focused into focus even when a photographic scene changes. <P>SOLUTION: The imaging apparatus performs focus adjustment while obtaining a focus signal indicating a focusing state based on image data obtained by imaging the subject by an imaging device 106. According to a command of a system controller 112, an AF processing part 105 drives a focus lens 103 based on the focus signal. The system controller 112 calculates temporal difference quantity in terms of luminance in a photographic image plane by using the image data obtained by imaging, and compares the difference quantity with a threshold to determine the state of the photographic scene. Monitoring the state is continued until the photographic scene is decided. When the photographic scene is decided, focus adjustment operation is performed immediately according to the command of the system controller 112. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an imaging apparatus and its focus control method, and more particularly to an automatic focus adjustment technique used for an electronic still camera, a video camera, and the like.

  Conventionally, in autofocus (hereinafter also referred to as AF) in a camera or the like, a contrast AF method is used in which a lens position at which a high frequency component of a luminance signal obtained by an imaging element is maximized is set as a focus position. . A scanning method is known as one of these methods. That is, an evaluation value (hereinafter also referred to as a focus evaluation value) based on the high frequency component of the luminance signal obtained from the image sensor while driving the lens over the entire focus detection range is calculated. The focus evaluation value is stored in the memory each time, and the lens position corresponding to the maximum value among the stored values becomes the focus position.

  A so-called hill-climbing method is known in which the lens is moved in the direction in which the focus evaluation value increases, and the position where the focus evaluation value is maximized is set as the in-focus position. This method is employed in an AF operation (hereinafter referred to as continuous AF) mode in which a focusing operation is repeated at a predetermined interval. Further, there is a method of reducing the AF operation time by limiting the AF focus detection range by the scanning method performed after the shooting preparation instruction by performing continuous AF before the shooting preparation instruction and maintaining the focused state. Japanese Patent Application Laid-Open No. 2004-228561 describes a moving direction when the focusing lens is moved next from a focus evaluation value calculated before moving the focusing lens of the photographing optical system by a predetermined amount and a focus evaluation value calculated after the movement. And a means for moving the focusing lens is disclosed.

Japanese Patent No. 4106485

  By the way, in continuous AF, when an attempt is made to move the lens in the direction in which the focus evaluation value increases, it is impossible to focus on an appropriate target unless the region to be focused on is known in the screen. Therefore, in continuous AF, the time required for the focusing operation is shortened by combining the scanning methods.

However, in the conventional apparatus, when the shooting scene changes, it is difficult to focus quickly on the subject to be focused. For example, if AF control is performed without determining a subject to be focused (hereinafter also referred to as a main subject) that the photographer intends to focus on the screen, the focus is adjusted depending on the shooting scene. There is a possibility that the subject cannot be brought into focus. Further, when the shooting scene changes, there is a possibility that the area of the subject to be focused in the shooting screen cannot be determined.
Therefore, an object of the present invention is to enable quick focusing on a subject to be focused even when a shooting scene changes.

In order to solve the above problems, the device according to the present invention is an imaging apparatus that performs focus adjustment to obtain a focus signal indicating a focus state based on the image data obtained by imaging a subject by the image pickup device, an instruction of photographing preparation A focus adjusting unit that performs a focus adjustment operation based on the focus signal, and a determination unit that determines the state of the shooting scene, the focus adjusting unit, before the shooting preparation instruction, In order to specify a subject area to be focused, a first focus adjustment operation that calculates the focus signal in a predetermined scan range and performs focus adjustment, and a first focus adjustment operation that performs focus adjustment on the higher one of the focus signals acquired sequentially. After the shooting preparation instruction, the focus signal is calculated in the scan range based on the specified subject area to be focused, and the focus adjustment is performed. Above By when the change of the photographic scene is detected the determination means in the second focus adjustment operation, performs the first focus adjustment operation.

  According to the present invention, it is possible to quickly focus on a subject to be focused even when a shooting scene changes.

It is a block diagram showing an example of composition of an imaging device concerning one embodiment of the present invention. 5 is a flowchart illustrating an automatic focusing control operation in the embodiment of the invention. It is a flowchart explaining the subroutine of the stability determination process in FIG. 3 is a flowchart for explaining a face detection AF scan subroutine in FIG. 2; 20 is a flowchart illustrating a subroutine for scene change determination in FIGS. 4, 10, 14, and 19. 16 is a flowchart for explaining a subroutine of focus determination processing in FIGS. 4, 11, and 15. It is a graph for demonstrating the method of the focus determination in FIG. FIG. 3 is a flowchart illustrating an AF scan subroutine for specifying a subject area in FIG. 2. FIG. It is a flowchart explaining the subroutine of the last reference determination in FIG. 10 is a flowchart for explaining a subroutine of a previous reference AF scan in FIG. 8. FIG. 15 is a flowchart for explaining a main subject area determination subroutine in FIGS. 10 and 14 and shows a first half of processing; FIG. 10 is a flowchart for explaining a main subject area determination subroutine, showing the latter half of the process. It is a figure explaining the process example of main subject area | region determination. FIG. 9 is a flowchart for describing a zone AF scan subroutine in FIG. 8. FIG. FIG. 15 is a flowchart for explaining a zone update determination subroutine in FIG. 14, showing the first half of the process. FIG. 15 is a flowchart for explaining a subroutine for zone update determination in FIG. 14 and shows the latter half of the process. FIG. It is a figure explaining the example of a process of zone update determination. FIG. 9 is a flowchart for explaining a focus driving subroutine in FIG. 8. FIG. 3 is a flowchart for explaining a subroutine of continuous AF in FIG. 2 and shows a first half of processing. FIG. 3 is a flowchart for explaining a subroutine of continuous AF in FIG. 2 and shows the latter half of the process. FIG. 3 is a flowchart illustrating a subroutine for determining scene instability in FIG. 2. It is a flowchart explaining the subroutine of AF for this exposure.

Hereinafter, an imaging apparatus and an in-focus control method according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration example of an electronic camera to which an embodiment of the present invention is applied. The photographing optical system includes a photographing lens 101 including a zoom mechanism, a diaphragm and shutter 102 for controlling the amount of light, and a focus lens 103 for focus adjustment.

  An AE (automatic exposure) processing unit 104 controls the aperture and shutter 102 in accordance with instructions from a system control unit described later. The AF processing unit 105 controls the focus lens 103 in accordance with an instruction from a system control unit described later, and performs automatic focus adjustment. The image sensor 106 is a photoelectric conversion unit that receives reflected light from a subject and converts it into an electrical signal, and its output is sent to an A / D converter 107.

  The A / D conversion unit 107 includes a CDS circuit that removes output noise and a non-linear amplification circuit that is performed before A / D conversion. The image processing unit 108 processes the output signal of the A / D conversion unit 107 and sends the signal to the AE processing unit 104 and a system control unit described later. The system control unit obtains a focus signal indicating an in-focus state based on the image data, and sends a control command to the AF processing unit 105 to control the focus adjustment operation. Image data from the image processing unit 108 is converted by the format conversion unit 109 and stored in the high-speed memory 110. For example, a random access memory (hereinafter referred to as DRAM) is used, and it is used as a high-speed buffer as temporary image storage means, a working memory for image compression / decompression, and the like. The image recording unit 111 includes a recording medium such as a memory card and its interface unit, and records image data on the recording medium.

  A system control unit 112 that controls the entire apparatus controls an imaging sequence and the like. An image display memory (hereinafter referred to as VRAM) 113 stores image data for displaying a captured image on the operation display unit 114. In addition to image display, the operation display unit 114 performs display for assisting operations and display of the camera state, and displays a captured image and a focus detection area at the time of shooting. Various processes described later are realized according to a program interpreted and executed by a CPU (central processing unit) constituting the system control unit 112.

  The operation unit 115 is a camera operation unit, and transmits various operation instructions to the system control unit 112. For example, there are a menu switch for performing various settings such as a shooting function of the image pickup apparatus and a setting at the time of image reproduction, a zoom lever for instructing a zoom operation of the shooting lens, an operation mode switching switch between a shooting mode and a playback mode, and the like. The shooting mode switch 116 is a switch for performing settings such as switching on / off of the face detection mode, and the instruction is sent to the system control unit 112. By operating the main switch 117, the system is turned on or turned off. The switch 118 is a switch (hereinafter referred to as SW1) for performing a shooting standby operation such as AF or AE, and the switch 119 is a shooting switch (hereinafter referred to as SW2) for performing shooting after the operation of SW1. .

  The face detection module 120 performs face detection using the image signal processed by the image processing unit 108. The one or more pieces of face information (position / size / reliability) detected here are sent to the system control unit 112. It should be noted that a known method can be used for face detection, and since it is not the main point of the present invention, detailed description is omitted.

  The moving object detection unit 121 is connected to the image processing unit 108, detects whether or not the subject and background in the shooting screen are moving, and sends moving object information to the system control unit 112. Specifically, among the image signals processed by the image processing unit 108, two images arranged in time series are compared, and moving object information (motion amount, position, range) of the subject and the background is obtained from the difference information of the luminance. ) Is detected.

  Next, the camera operation will be described with reference to the flowchart of FIG. First, in S201, the system control unit 112 determines the state (ON / OFF) of SW1 instructing preparation for photographing. As a result, when the state of SW1 is ON (on), the process proceeds to S212, and when it is OFF (off), the process proceeds to S202. In S202, a scene stability determination is performed. This is a process for determining whether or not the shooting scene is stable, and details of the procedure will be described later. In S203, the system control unit 112 checks whether or not the shooting scene is determined to be stable in S202. When the stability is determined, the return value is TRUE (true), and when it is determined that the shooting scene is not stable, the return value is FALSE (false). In the case of TRUE, the process proceeds to S204, and in the case of FALSE, the process returns to S201. The state where the shooting scene is stable is that the state of the subject to be shot and the camera are stably maintained and are in a state suitable for shooting. When it is determined that the shooting scene is not stable and the scene is not fixed, it is desirable to stop the focus lens 103 without driving it.

  In S204, the system control unit 112 determines whether or not the subject brightness is equal to or lower than a predetermined value. As a result, if the subject brightness is equal to or lower than the predetermined value, the process proceeds to S205, but if not, the process proceeds to S206. In S205, an AF frame for low illumination is set. Here, the AF frame is an area for acquiring a focus evaluation value in the photographing screen. The focus evaluation value is a value obtained by converting the analog video signal read from the image sensor 106 into a digital signal by the A / D converter 107 and extracting the high frequency component of the luminance signal from the output from the output. It is. Data indicating this value is stored in the built-in memory by the system control unit 112 in association with the position of the focus lens 103 and the AF frame position. “Obtain a focus evaluation value” means that the AF processing unit 105 reads out the focus evaluation value stored in the memory by the system control unit 112 for determination in AF control. Since the exposure time is extended at low illuminance, AF accuracy in scanning cannot be ensured. Therefore, in the present embodiment, at the time of low illuminance, scanning at the time of subject area specification or face detection is not performed, and one AF frame having a predetermined size is set near the center of the screen.

In S206, the face detection module 120 checks whether face detection has been performed. If face detection has been performed, the process proceeds to S207. If face detection has not been performed, the process proceeds to S208. In S207, a face detection AF scan is performed, and this process is executed according to a procedure to be described later, and then the process proceeds to S209. In S208, AF scan processing for specifying a subject area is executed, and details of the procedure will be described later. After S205, S207, and S208, the process proceeds to S209, where the continuous AF process is executed, and details of the procedure will be described later. In step S210, a scene instability determination process is executed. This is a process of determining whether or not the shooting scene is unstable, and details of the procedure will be described later. In S211, the system control unit 112 determines whether the shooting scene is unstable. If it is determined that the shooting scene is unstable, the process returns to S201. If it is determined that it is not unstable, the process returns to S209. Here, “the photographing scene is unstable” means that the state of the subject to be photographed and the state of the camera are unstable and are not suitable for photographing.
When the process proceeds from S201 to S212, the focus degree determination flag is set to FALSE. In the next S213, the photographing process is performed according to the procedure described later, and then the process returns to S201.

  As described above, the system control unit 112 continues to monitor the state until the shooting scene becomes stable and the shooting scene is determined, and performs the focus adjustment operation when the shooting scene is determined. Control. Note that the AE operation is always performed in parallel with the above-described operation. In this case, the AE processing unit 104 controls the aperture and the shutter 102 based on the control signal from the system control unit 112 so that the brightness of the image displayed on the operation display unit 114 is appropriate.

  Next, the scene stability determination of S202 shown in FIG. 2 will be described using the flowchart of FIG. First, in S301, the system control unit 112 acquires a luminance difference amount between two pieces of image data output from the moving object detection unit 121 of FIG. This represents a temporal difference amount related to the luminance in the photographing screen, that is, a luminance difference between images at different times. In next step S302, the system control unit 112 performs a filtering process on the luminance difference amount obtained in step S301, and performs a process of removing a noise component and extracting a feature amount of a subject image. In S303, a threshold corresponding to the current screen brightness is set. This threshold value is a reference value used for determining the stability of the shooting scene, and may be determined not only by the brightness of the screen but also by the shutter speed, aperture value, sensitivity, and other shooting conditions. In S304, the luminance difference amount obtained in S302 is compared with the threshold set in S303. As a result, if the luminance difference value is greater than or equal to the threshold value, the process proceeds to S305. At the present time, it is determined that the shooting scene has not been determined by the user and is not in a stable state, FALSE is returned as a return value, and the process ends. On the other hand, if the luminance difference value is smaller than the threshold value, the process proceeds to S306. The user has determined the shooting scene, and is determined to be in a stable state, returns TRUE as a return value, and the process ends.

  Next, the face detection AF scan of S207 shown in FIG. 2 will be described using the flowchart of FIG. First, in step S401, the system control unit 112 performs AF frame setting based on face information (position / size) detected by the face detection module 120. In S402, the AF processing unit 105 moves the focus lens 103 to the scan start position. Here, the scan start position is determined based on the distance to the person estimated from the detected face size, for example. In step S <b> 403, the system control unit 112 acquires focus evaluation value data at the current focus lens position and stores the data in the DRAM 110. In S404, the current position of the focus lens 103 is acquired, and the system control unit 112 stores the data of the position in the DRAM 110. In step S405, the system control unit 112 determines the state (ON / OFF) of SW1 that instructs preparation for shooting. If this state is the ON state, this process is terminated and the process proceeds to S212 (see node A) in FIG. 2, but if it is the OFF state, the process proceeds to S406. In S406, scene change determination is executed according to the procedure described later. This scene change determination is a process for determining whether or not the shooting scene has changed from the state of the camera or the state of the subject.

In step S407, the system control unit 112 determines whether the current position of the focus lens 103 is equal to the scan end position. As a result, if both are equal, the process proceeds to S409, but if not, the process proceeds to S408. The scan end position is determined based on, for example, the distance to the person estimated from the detected face size. In S408, the AF processing unit 105 moves the focus lens 103 by a predetermined amount in the scan end direction, and then returns to S403. In step S409, focus determination is performed according to a procedure described later. In S410, the system control unit 112 checks whether or not the result of the focus determination in S409 is “good”. Here, “◯ determination” is defined as a determination result obtained when the contrast of the subject is sufficient and the subject exists within the scanned distance range. If the determination result is ◯, the process proceeds to S411, and if not, the process proceeds to S414.
In S411, a process for calculating an in-focus position where the focus evaluation value acquired in S403 reaches a peak is performed. In step S412, the AF processing unit 105 moves the focus lens 103 to the in-focus position calculated in step S411. In S413, the peak detection flag is set to TRUE.

  On the other hand, when the process proceeds from S410 to S414, it is not “good” determination, that is, the contrast of the subject is insufficient, or the subject exists outside the scanned distance range. The AF processing unit 105 moves the focus lens 103 to a position (fixed point) indicated by data stored in the DRAM 110 in advance. Here, the fixed point is set to a distance with a high probability of existence of the subject. For example, if a face is detected, the distance to the person estimated from the size of the detected face is used. After S413 and S414, return processing is performed.

  Next, scene change determination will be described using the flowchart of FIG. This determination is a predefined process performed in S406 of FIG. 4, S1106 of FIG. 10, which will be described later, S1405 of FIG. 14, and S2107 of FIG. First, in step S501, the system control unit 112 checks whether the face detection state detected by the face detection module 120 has changed. If the face detection state has changed, this determination process is terminated, and the process returns to S201 (see node B) in FIG. If the face detection state has not changed, the process proceeds to S502. “Face detection state” means whether or not a face is detected. For example, if the face is detected at the previous scene change determination and the face is not detected at the current scene change determination, the face detection state has changed.

  In step S <b> 502, the system control unit 112 checks whether or not the amount by which the camera is shaken in a specific direction (hereinafter referred to as camera movement amount) is equal to or greater than a predetermined amount. If the camera movement amount is equal to or greater than the predetermined amount and the determination result is unstable, the determination process is terminated and the process returns to S201 in FIG. 2, but if not, the process proceeds to S503.

  In step S503, the system control unit 112 determines whether continuous AF is being performed. In the case of continuous AF, the process proceeds to S504, which is a process for determining whether or not the subject luminance difference is equal to or smaller than a predetermined value (reference value). The “subject brightness difference” is a difference between the subject brightness value acquired at the previous scene change determination and the subject brightness value detected at the current scene change determination. If the difference between the subject luminance values is greater than the predetermined value, it is determined that the shooting scene has changed, the determination process ends, and the process returns to S201 in FIG. On the other hand, if the subject luminance difference is equal to or smaller than the predetermined value, the determination process is terminated and the return process is performed.

  If it is determined in S503 that the continuous AF is not in progress, the process proceeds to S505. Here, the system control unit 112 determines whether or not the exposure time is equal to or longer than a predetermined time. If the exposure time is equal to or longer than the predetermined time, the determination process ends and the process returns to S201 in FIG. That is, when the exposure time is equal to or longer than the predetermined time, the interval for acquiring the focus evaluation value is extended, so that the AF control accuracy cannot be ensured. On the other hand, if the exposure time is less than the predetermined time, the process proceeds to S506. Here, the system control unit 112 checks whether or not the state of the diaphragm 102 has changed. If the state of the aperture 102 has changed, the process proceeds to S507, but if it has not changed, this determination process ends and the process returns. In the present embodiment, the case of using the aperture control has been described. However, when exposure control is performed using an ND filter instead of the aperture control, a change in the state of the ND filter may be determined. This is because the peak position of the focus evaluation value changes when the state of the diaphragm or the ND filter changes.

  S507 is processing for determining whether or not the face detection module 120 detects a face. If the system control unit 112 determines that the face of the person who is the subject has been detected, the system control unit 112 ends the determination process and proceeds to S402 (see node D) in FIG. If it is determined that no face has been detected, the process ends and the process proceeds to S809 (see node C) in FIG.

  Next, an in-focus determination subroutine will be described with reference to the flowchart of FIG. 6 and the graph of FIG. This process is a predefined process performed in S409 of FIG. 4, S1201 of FIG. 11 described later, and S1501 of FIG. As shown in FIG. 7, the focus evaluation value has a mountain shape, with the focus lens position on the horizontal axis and the focus evaluation value on the vertical axis, as shown in FIG. Therefore, based on the difference between the maximum value and the minimum value of the focus evaluation value, the length of the portion that is inclined with a certain value (this is referred to as “SlopeThr”), and the slope of the inclined portion, the shape of the mountain is determined. By determining, focus determination can be performed.

The in-focus determination result is output as one of the following three items including the above-described ○ determination.
Judgment: Judgment result when the subject has sufficient contrast and the subject is located at a distance within the scanned distance range.
X Determination: Determination result when the subject has insufficient contrast or the subject is located at a distance outside the scanned distance range.
Δ Determination: The determination result when the subject is located outside the distance range scanned in the closest direction in the X determination.

Definition of each quantity with reference to FIG. 7, where L is the length of the sloped portion with an inclination greater than a certain value, and SL / L is the average slope of the sloped portion for judging the shape of the mountain Will be explained. In the figure, the point where it is recognized that the slope continues from the top of the mountain (point A) is D point (left side) and point E (right side), and the width from point D to point E is the width L of the mountain. . The range in which the inclination is recognized to be continued is a range in which the focus evaluation value decreases from the point A over a predetermined amount, that is, SlopeThr or more, and the scan point continues. The “scan point” is a point at which a focus evaluation value is acquired while the focus lens is continuously moved while the lens moves from the scan start point to the scan end point.
The difference between the focus evaluation value at point A and the focus evaluation value at point D is denoted SL1, and the difference SL2 between the focus evaluation value at point A and the focus evaluation value at point E is denoted as SL1 + SL2. "Is SL.

The focus determination will be described with reference to the flowchart of FIG. First, in step S601, the system control unit 112 obtains the maximum value (Max) and the minimum value (Min) of the focus evaluation value. Next, in step S602, obtains a scan point (Max Point) at which the focus evaluation value is maximum, and the process proceeds to step S603. Here, the system control unit 112 obtains L and SL for judging the shape of the mountain from the scan point and the focus evaluation value, and obtains SL / L. The next step S604 is a process for determining whether or not the mountain shape stops climbing to the closest side. The system controller 112 determines that the climb to the near side is stopped when both of the following two conditions are satisfied.
The scan point with the maximum focus evaluation value is the near end in the predetermined range where the scan was performed.
The difference between the focus evaluation value at the near-end scan point and the focus evaluation value at the scan point that is one point closer to infinity from the near-end scan point is greater than or equal to a predetermined reference value.

If it is determined that the climb to the closest side is stopped, the process proceeds to S609. Otherwise, the process proceeds to S605. Here, the system control unit 112 determines whether or not the mountain shape stops climbing to the infinity side. It is determined that the climb to the infinity side is stopped when both of the following two conditions are satisfied.
The scan point that is the maximum focus evaluation value is the infinity end in the predetermined range where the scan was performed.
The difference between the focus evaluation value at the scan point at the infinity end and the focus evaluation value at the scan point closer to the closest end by one point from the scan point at the infinity end is greater than or equal to a predetermined reference value.

If it is determined that the climb to the infinity side is stopped, the process proceeds to S608. Otherwise, the process proceeds to S606. Here, the system control unit 112 determines whether or not both of the following three conditions are satisfied.
-The length L of the portion inclined at a certain inclination or more is not less than a predetermined reference value.
The average slope SL / L of the inclined part is not less than a predetermined reference value.
-The difference between the maximum value (Max) and the minimum value (Min) of the focus evaluation value is greater than or equal to a predetermined reference value.

  If all of these conditions are satisfied, the process proceeds to S607. If even one of the conditions is not satisfied, the process proceeds to S608. The determination result is “Yes” in S607, “No” in S608, and “No” in S609. That is, in S607, the obtained focus evaluation value has a mountain shape, the subject has sufficient contrast, and focus adjustment is possible, and therefore the system control unit 112 sets the determination result as “good”. On the other hand, in S608, since the obtained focus evaluation value is not mountain-shaped and the subject contrast is insufficient and focus adjustment is impossible, the system control unit 112 determines the determination result as x determination. And In S609, although the obtained focus evaluation value is not mountain-shaped, it is in a state of continuing to climb in the near-end direction, and there is a possibility that a subject peak exists on the near side. The system control unit 112 sets the determination result as Δ.

  Next, the process of S208 shown in FIG. 2, that is, the AF scan for specifying the subject area will be described with reference to the flowchart of FIG. Here, AF scanning is performed to identify the area of the main subject in the shooting screen.

  First, in step S801, the system control unit 112 determines whether electronic zoom is being performed. If it is determined that the electronic zoom is being performed, the process proceeds to S802. If the electronic zoom is not being performed, the process proceeds to S803. In S802, AF frame setting for electronic zoom is performed. Here, “electronic zoom” means to enlarge the central area of the screen and display it on the operation display unit 114. Since the image is enlarged, the number of pixels of the image displayed on the operation display unit 114 is smaller than that when the electronic zoom is not performed. Therefore, if the AF frame is set so that the ratio of the image displayed on the operation display unit 114 during the electronic zoom is the same as when the electronic zoom is not performed, the case where the electronic zoom is performed is compared to the case where the electronic zoom is not performed. The number of pixels in the AF frame is reduced. Therefore, the S / N ratio of the focus evaluation value decreases. For this reason, it is necessary to change the AF frame setting method between when the electronic zoom is performed and when the electronic zoom is not performed. In the present embodiment, at the time of electronic zoom, one AF frame having a predetermined size is set near the center of the shooting screen.

  In S803, N × N AF frames are set in the screen. For example, when N = 5 and the size of the AF frame is 10% of the shooting screen in both vertical and horizontal lengths, the AF frame setting shown in FIG. 13 is obtained. The N value or the size of the AF frame can be set in consideration of the existence probability of the main subject in the screen. Further, the number of AF frames may be different between the horizontal direction and the vertical direction.

  In the next S804, the previous reference determination is performed, and the procedure will be described later. In step S805, as a result of the previous reference determination in step S804, the system control unit 112 determines whether there is a change between the previous shooting scene and the current shooting scene. As a result, when it is determined that the scene does not change much between the previous time and the current time, the process proceeds to S806, and when it is determined that the scene has changed, the process proceeds to S809. In S806, the previous reference AF scan is performed, and the procedure will be described later. In step S807, it is determined whether the main subject area has been identified in the previous reference AF scan in step S806. As a result, if the main subject area can be identified, the process proceeds to S808, but if not, the process proceeds to S809. After the peak detection flag is set to TRUE in S808, the process proceeds to S813.

  In step S809, zone AF scanning is performed according to a procedure described later. The next step S810 is a process for determining whether or not the main subject area has been identified in the zone AF scan in step S809. If the main subject area can be identified, the process proceeds to S808, and if it cannot be identified, the process proceeds to S811. In step S811, uniform surface determination processing is performed to determine whether there is a “uniform surface state”. The “state that is a uniform surface” is a state in which there is no brightness difference in the screen and there is no contrast, so that a focus evaluation value peak cannot be obtained sufficiently even when AF control is performed. If the AF scan shown in S208 of FIG. 2 is repeated each time the shooting scene is stabilized in this state, the focus variation on the screen is repeated unnecessarily, which is troublesome. Thus, when it is determined that the state is a uniform surface, it is desirable to stop the focus lens 103 until the determination of the state is not made. Note that description of the details of the uniform surface determination process is omitted.

  If the main subject area cannot be identified in the zone AF scan in S809, in S812, processing for setting an AF frame in a predetermined area set in advance in the shooting screen is performed. Here, as the AF frame of the predetermined area, for example, one frame in the central area of the shooting screen is set, and it is desirable to set the AF frame in a highly likely area where the main subject exists. Then, the process proceeds to S813, and after the focus drive is performed according to the procedure described later, the return process is performed.

  Next, the previous reference determination of S804 shown in FIG. 8 will be described using the flowchart of FIG. This process is a process for determining whether or not the current shooting scene has changed much with respect to the shooting scene in which the previous AF scan was performed.

  First, in step S1001, the system control unit 112 checks whether the main subject area has been specified in the previous AF scan. As a result, if the main subject area can be identified, the process proceeds to S1002, and if the area cannot be identified, the process proceeds to S1005. In S1002, it is determined whether or not the current position of the focus lens 103 is closer to the predetermined position. As a result, if the current position of the focus lens 103 is closer to the predetermined position, the process proceeds to S1003, and if not, the process proceeds to S1005. In S1002, it is determined whether or not the current position of the focus lens 103 is closer to the predetermined position, but it may be determined whether or not the current position of the focus lens 103 is on the infinity side from the predetermined position.

  In S1003, it is determined whether or not the time difference between the previous and current AF scans, that is, the elapsed time from the previous time is within a predetermined time. As a result, if it is within a predetermined time from the time of the previous AF scan, the process proceeds to S1004, but if not, the process proceeds to S1005. In S1004, it is determined that the shooting scene in the previous AF scan is not so different. In S1005, it is determined that the shooting scene has changed significantly since the previous AF scan. After S1004 and S1005, the determination process ends, and a return process is performed.

  Next, the previous reference AF scan of S806 shown in FIG. 8 will be described using the flowchart of FIG. First, in S1101, the scan range centering on the current position of the focus lens 103 is set to a first range (indicated by a numeral 1 in a circle). Here, since it is determined in the previous reference determination that the shooting scene does not change much between the previous time and the current time, the first scan range is a narrow range. In step S1102, the AF processing unit 105 that has received a command from the system control unit 112 moves the focus lens 103 to the scan start position. In S1103, the A / D conversion unit 107 converts the analog video signal read from the image sensor 106 into a digital signal. The image processing unit 108 extracts a high-frequency component of the luminance signal from this signal, and the system control unit 112 stores it in the memory as focus evaluation value data. In step S1104, the current position of the focus lens 103 is acquired, and the system control unit 112 stores the data of the position in the memory. In step S1105, the system control unit 112 determines the state (ON / OFF) of SW1 that instructs to prepare for shooting. If the state is ON, the process ends and the process proceeds to step S212 (see node A) in FIG. . If SW1 is OFF, the process proceeds to S1106. After the scene change determination described above is performed in S1106, the system control unit 112 determines whether the current position of the focus lens 103 is equal to the scan end position in S1107. If both positions are equal, the process proceeds to S1108. If both positions are different, the process proceeds to S1109. In S1108, after the main subject area determination described later is performed, the return process is performed. In S1109, the AF processing unit 105 moves the focus lens 103 by a predetermined amount in the scan end direction, and the process returns to S1103.

  Next, main subject area determination will be described with reference to the flowcharts of FIGS. This process is a predefined process performed in S1108 shown in FIG. 10 or S1411 in FIG. 14 described later, and it is determined whether or not the main subject area in the shooting screen has been identified. FIG. 13 is an explanatory diagram of a processing example of main subject area determination. In this example, the AF frame size is 10% of the screen, N = 5, the scan range is 0 to 500, and the predetermined depth range is ± 10. The numerical values indicating the scan range and the predetermined depth range represent the position of the focus lens 103. This indicates that when a stepping motor is used as the driving motor for the focus lens 103 (not shown), the position corresponding to the number of driving pulses is large and the position where the value is large is on the near side.

First, in S1201 of FIG. 11, the above-described focus determination is performed in all the set AF frames. For example, it is assumed that the focus determination result shown in FIG. 13A is obtained in each AF frame. In this example, the determination results in the topmost AF frame are all X determinations, and in the second line from the top, there are two ◯ determinations and three X determinations, and in the third line, four ◯ determinations and one X determination. It is judged. The determination result in the AF frame for the lower two lines is “good”.
In S1202, the peak position of the focus evaluation value in each AF frame (hereinafter referred to as PeakPos) is calculated and stored in the memory. For example, as shown in FIG. 13B, the peak position calculation result indicated by a numerical value, that is, the value of PeakPos is shown in each of the AF frames at the position where the circle is determined. In step S1203, it is determined whether or not the set AF frame is one frame. If the set AF frame is one frame, the process proceeds to S1214, but if it is not one frame, the process proceeds to S1204. Here, processing for sorting PeakPos values in each AF frame of the center M × M frame in ascending order is performed. The number sorted here is denoted as S. In the following description, M = 3. In the example of FIG. 13, a total of nine frames including three vertical frames and three horizontal frames surrounded by a thick line indicate each AF frame. Here, since the peak position cannot be calculated in the AF frame determined to be x in the focus determination in S1201, it is not included in the sorting target. In the example shown in FIG. 13B, the peak positions in the nine frames are “100, 90, 400, 400, 100, 410, 400, 100” from the upper left corner to the lower right corner. Sorted as “410, 400, 400, 400, 100, 100, 100, 90” in the closest order, and the sort number S = 8. In S1205, the value of the counter P indicating the closest order of the peak positions in the M × M frame calculated in S1202 is set to the initial value 1. In step S1206, the P-th PeakPos in the sort order is set to “PeakPosP” (“P” represents a natural number variable). For example, in FIG. 13B, when P = 1, PeakPosP = 410.

  In S1207, a process of detecting “a lump” of AF frames satisfying a predetermined condition is executed, and the number of AF frames constituting the “a lump” and the positions of the respective AF frames are stored in the memory. Here, “chunk” means a group in which AF frames in a predetermined depth range with respect to PeakPosP are grouped together in a central M × M AF frame, and a circle is determined. In other words, “a lump” is a set of AF frames in a state where the AF frames satisfying the above condition are adjacent vertically and horizontally. When there are a plurality of “chunks”, one of the “chunks” can be selected based on the number of AF frames constituting the “chunk” and the position of the “chunks”.

  In S1208, the determination result is ◯ determination so that one or more of the central M × M AF frames are included in the central N × N AF frames, and within a predetermined depth with respect to PeakPosP. A process of detecting “a lump” is performed. Then, data indicating the number of AF frames constituting the detected “lumps” and the position of each AF frame is stored in the memory. For example, with respect to the determination results shown in FIGS. 13 (a) and 13 (b), the value of PeakPosP is set to 400 or more in the “lumps” shown in gray frames in FIG. A group of AF frames is detected. Then, the process proceeds to S1209 (see node F) in FIG.

  When the process proceeds from S1203 to S1214, it is determined whether or not the focus determination result at S1201 is a ◯ determination. If the determination is ◯, the process proceeds to S1215 (see node G) in FIG. The process proceeds to S1217 (see node H) in FIG.

  In S1209 of FIG. 12, a determination process is performed to determine whether or not the “chunk” detected in S1207 or S1208 of FIG. 11 is a “chunk” including the center frame. As a result, if it is determined that the “chunk” including the central frame is made, the process proceeds to S1215; otherwise, the process proceeds to S1210. In S1210, a determination process is performed to determine whether the “chunk” detected in S1207 or S1208 is a “chunk” that includes a predetermined number or more of AF frames within the M × M frame. If a positive determination result is obtained, the process proceeds to S1215. If a negative determination result is obtained, the process proceeds to S1211. In S1211, whether or not the “chunk” detected in S1207 or S1208 is a “chunk” that includes one or more of the central M × M frames and includes a predetermined number or more of the AF frames in the N × N frame. Judgment processing is performed. If a positive determination result is obtained, the process proceeds to S1215. If a negative determination result is obtained, the process proceeds to S1212. In S1212, the counter P is incremented, and 1 is added to the P value. In S1213, the value of the counter P is compared with the sort number S. If the P value is larger than the S value, the process proceeds to S1217. If the P value is equal to or smaller than the S value, the process proceeds to S1206 (see node I) in FIG. Return.

  After it is determined in S1215 that the main subject area has been specified, in S1216, each AF frame constituting the “chunk” is determined to be the main subject area, and these are selected, and this determination process ends. Note that when one AF frame is set here, processing for selecting the one frame is performed. On the other hand, after it is determined in S1217 that the main subject area cannot be specified, this determination process ends.

  Next, the zone AF scan of S809 shown in FIG. 8 will be described using the flowchart of FIG. Here, the “zone” refers to individual ranges when the focusable distance range is divided into a plurality of ranges.

  In step S1401, the AF processing unit 105 moves the focus lens 103 to the scan start position in accordance with an instruction from the system control unit 112. Here, the scan start position is, for example, the infinity end position. In S1402, the analog video signal read from the image sensor 106 is converted into a digital signal by the A / D conversion unit 107, and the image processing unit 108 extracts a high-frequency component of the luminance signal from the output. The system control unit 112 stores this in the memory as focus evaluation value data. In step S1403, the current position of the focus lens 103 is acquired, and the system control unit 112 stores the position data in the memory. In step S <b> 1404, the system control unit 112 determines the state (ON / OFF) of SW <b> 1 that instructs preparation for shooting. If this state is the ON state, this process is terminated and the process proceeds to S212 (see node A) in FIG. 2, and if it is the OFF state, the process proceeds to S1405. In S1405, the scene change determination described above is performed, and in S1406, it is determined whether or not the focus lens 103 is at a preset zone boundary position. If the result is affirmative, the process proceeds to S1407. If the result is negative, the process proceeds to S1409.

  In S1407, zone update determination is performed, and the procedure will be described later. Here, “zone update” refers to continuing scanning of a zone adjacent to the zone after scanning of a certain zone. In S1408, the system control unit 112 determines whether or not to perform zone update as a result of the determination in S1407. If zone update is to be performed, the process proceeds to S1409. If zone update is not to be performed, the process proceeds to S1411. In step S1409, the system control unit 112 checks whether or not the current position of the focus lens 103 is equal to the scan end position. If both positions are equal, the process proceeds to step S1411. If both positions are different, the process proceeds to step S1410. In S1410, the AF processing unit 105 moves the focus lens 103 by a predetermined amount in the scan end direction, and then returns to S1402. In S1411, after the above-described main subject area determination is performed, return processing is performed.

  Next, the zone update determination in S1407 shown in FIG. 14 will be described using the flowcharts of FIGS. This process is a process for determining whether or not there is a high probability that the main subject exists ahead in the scan direction, that is, whether or not to continue the AF scan. FIG. 17 is a diagram for explaining an example of zone update determination. In this example, the size of the AF frame is 10% of the screen, and N = 5 and M = 3.

  First, in S1501 in FIG. 15, the above-described focus determination is performed in all the set AF frames. For example, it is assumed that the focus determination result shown in FIG. 17A is obtained in each AF frame. In this example, the determination results at six locations in the left corner are Δ determinations. In addition, the determination results for the two rows from the top and the determination results at the two right locations on the third row are “x” determinations, and “good” determinations are made at other locations. In S1502, it is determined whether or not the scan has been performed up to the final zone. If the scan has been performed up to the final zone, the process proceeds to S1512 (see node Q) in FIG. 16, but otherwise the process proceeds to S1503. Here, a determination is made as to whether or not the determination result has a frame for determination. If there is a judgment frame, the process proceeds to S1504, and if there is no judgment frame, the process proceeds to S1511 (see node J) in FIG. S1504 is a determination process of whether or not the determination result of the center frame is Δ determination. If the determination result of the center frame is Δ, the process proceeds to S1511 in FIG. 16, and if not, the process proceeds to S1505. In S1505, the number of frames for which the determination result is Δ in the central M × M frame is counted. It is determined whether or not there is a “cluster” in which the number of frames determined to be Δ is greater than or equal to a predetermined number of frames. In the example of FIG. 17, in the 3 × 3 central frame, the number of Δ determination frames is 2, and the predetermined number of frames is 2. Δ If the number of frames for determination is equal to or greater than the predetermined number of frames, the process proceeds to S1511 in FIG.

  In step S1506, it is determined whether or not there is a “chunk” that is greater than or equal to the predetermined number of frames in the N × N AF frames so that one or more of the central M × M frames are included. In the example of FIG. 17, the predetermined number of frames is four. ΔThere are six frames for determination, and two frames of the “lumps” are included in the central frame. In this case, the process proceeds to S1511 in FIG. On the other hand, if the determination condition is not satisfied, the process proceeds to S1507 (see node K) in FIG.

  In S1507, the ◯ determination frames in the center M × M frame are counted. It is determined whether or not there is a “chunk” whose number of frames is equal to or greater than a predetermined number. If such a “chunk” exists, the process proceeds to S1512. If there is no “chunk”, the process proceeds to S1508. In the example of FIG. 17, if there are three “◯” determination frames in the center frame and the predetermined number is five, the above determination condition is not satisfied. S1508 is a process for determining whether or not the determination result of the center frame is x determination. If the determination result of the center frame is x, the process proceeds to S1511. Otherwise, the process proceeds to S1509. In S1509, it is determined whether or not there is a “cluster” in which the number of frames for Δ determination or × determination in the central M × M frame is equal to or larger than the predetermined number of frames. If there is such a “chunk”, the process proceeds to S1511, and if not, the process proceeds to S1510. If the predetermined number of frames is 2 in the example of FIG. 17, the number of frames for determination Δ is 2 and the number of frames for determination x is 4 in the central frame, so the above determination condition is satisfied. In S1510, a determination is made as to whether or not there is a “chunk” in which all of the N × N frames have a Δ determination or X determination frame number exceeding a predetermined number so as to include one or more of the central M × M frames. Is done. If such a “chunk” exists, the process proceeds to S1511. If no “chunk” exists, the process proceeds to S1512. In FIG. 17, for example, if the predetermined number is 4, the number of frames constituting the “group” of Δ determination is 6, the number of Δ determination frames is 2 in the center frame, and the determination condition is as follows. be satisfied. In S1511, the determination “update zone” is made, and the determination “do not update zone” is made in S1512. For example, when N = 5 and M = 3, the “mass” of the Δ determination satisfies the above determination condition in the gray area in FIG. 17B, and it is determined to “update the zone” in S1511. After S1511 and S1512, return processing is performed.

  Next, focus driving in S813 in FIG. 8 will be described using the flowchart in FIG. First, in S2001, it is determined whether or not the main subject area can be specified. If the area can be specified, the process proceeds to S2002. If not, the process proceeds to S2003. In S2002, the focus lens 103 is driven to the closest position in the selected AF frame. In S2003, it is determined whether or not there is an AF frame for ◯ determination in the center M × M frame. As a result, if there is an AF frame for ◯ determination, the process proceeds to S2004, but if not, the process proceeds to S2005. In S2004, the focus lens 103 is driven to the closest position in the AF frame determined as ◯ in the center M × M frame. In S2005, control is performed to move the focus lens 103 to a previously stored position (fixed point). Here, the “fixed point” is set, for example, at a position corresponding to a distance where the existence probability of the subject is high. After S2002, S2004, and S2005, this process ends and a return process is performed.

  Next, the continuous AF of S209 shown in FIG. 2 will be described using the flowcharts of FIGS. First, in S2101 of FIG. 19, the focus degree determination flag is set to TRUE. In step S2102, focus evaluation value acquisition processing for each set AF frame is performed. In S2103, it is determined whether or not the set AF frame is one frame. If the AF frame is one frame, the process proceeds to S2105. Otherwise, the process proceeds to S2104. In S2104, the evaluation value calculated using the focus evaluation value of the AF frame selected as the main subject region is reset as the focus evaluation value used in S2105 and thereafter. Thereby, even if the shooting scene changes and the main subject area in the screen changes, the focus evaluation value of the main subject area in the screen can always be calculated.

  In S2105, the degree of focus is calculated based on the focus evaluation value. For example, the degree of focus is determined in three stages of high, medium, and low based on the focus evaluation value. In S2106, the system control unit 112 determines the state (ON / OFF) of SW1 that instructs to prepare for photographing. If the state is ON, the process is terminated and the process proceeds to S213 (see node E) in FIG. . When SW1 is in the OFF state, the process proceeds to S2107, and the scene change determination described above is performed. In S2108, it is determined whether or not the peak detection flag is TRUE. If TRUE, the process proceeds to S2125 (see node S) in FIG. 20, and if FALSE, the process proceeds to S2109 (see node R) in FIG.

  In S2109, the current position of the focus lens 103 is acquired. In S2110, 1 is added to the value of the acquisition counter. The “acquisition counter” is a counter for counting the number of acquired focus evaluation values and the number of acquired current positions of the focus lens 103. It is assumed that the value of this acquisition counter is set to zero in advance in the initialization operation. In S2111, the value of the acquisition counter is compared with 1. If the value is 1, the process proceeds to S2114. If the value of the acquisition counter is not 1, the process proceeds to S2112.

  In S2112, the current focus evaluation value is compared with the previous focus evaluation value. If the current focus evaluation value is larger than the previous focus evaluation value, the process proceeds to S2113; otherwise, the process proceeds to S2120. In S2113, 1 is added to the value of the increment counter. The “increase counter” is a counter for counting the number of times when it is determined that the current focus evaluation value is larger than the previous time. In S2114, the system control unit 112 sets the current focus evaluation value as the maximum value of the focus evaluation value, and then sets the current position of the focus lens 103 as the peak position of the focus evaluation value in S2115. In step S <b> 2116, the system control unit 112 resets the current focus evaluation value as the previous focus evaluation value. Data indicating the focus evaluation values in S2114 to S2116 is stored in a calculation memory built in the system control unit 112. In S2117, it is determined whether or not the current position of the focus lens 103 is at the end of the focus detection range. If the current position is the end position, the process proceeds to S2118; otherwise, the process proceeds to S2119. In S2118, the moving direction of the focus lens 103 is reversed in accordance with a command from the system control unit 112, and in S2119, the focus lens 103 is moved by a predetermined amount. Then, return processing is performed.

  When the processing proceeds from S2112 to S2120, the difference between the peak evaluation value and the current evaluation value, that is, “the maximum value of the focus evaluation value−the current focus evaluation value” is compared with a predetermined amount. If “the maximum value of the focus evaluation value—the current focus evaluation value” is larger than the predetermined amount, the process proceeds to S2121; otherwise, the process proceeds to S2116. In S2120, if “the maximum value of the focus evaluation value−the current focus evaluation value” is larger than the predetermined amount, that is, if the focus evaluation value has decreased by a predetermined amount from the maximum value, the maximum value is set at the focus peak position. It is considered as the value of. In S2121, it is determined whether or not the value of the increment counter is greater than zero. If the value is greater than zero, the process proceeds to S2122, and if it is zero, the process proceeds to S2116. In S2122, the focus lens 103 moves to the peak position in S2115, that is, the peak position at which the stored focus evaluation value becomes the maximum value. In S2123, after the peak detection flag is set to TRUE, in S2124, the value of the acquisition counter is set to zero, and the process proceeds to S2119.

S2125 (refer to node S) is a determination process as to whether or not the current focus evaluation value has changed by a predetermined ratio or more with respect to the maximum value of the focus evaluation value. If a large fluctuation over a predetermined ratio has occurred, the process proceeds to S2127, and if a small fluctuation less than the predetermined ratio, the process proceeds to S2126. In S2126, the focus lens 103 stops at that position, and the process proceeds to S2119. In S2127, the peak detection flag is set to FALSE, and the maximum focus evaluation value and the peak position are reset. This is because the focus lens position where the focus evaluation value is maximized is searched again. Then, after the increment counter is reset in S2128, the process proceeds to S2119.
As described above, the drive control of the focus lens 103 is performed so that the focused state is always obtained with respect to the main subject in the continuous AF operation.

Next, the scene instability determination of S210 shown in FIG. 2 will be described using the flowchart of FIG. First, in step S <b> 2201, the system control unit 112 acquires a luminance difference amount between image data based on the data related to the two images output from the moving object detection unit 121 in FIG. 1. Next, in S2202, noise component removal and subject image feature value extraction are performed by performing filter processing on the luminance difference amount obtained in S2201. In S2203, a threshold value corresponding to the current screen brightness is set. The threshold value for determining instability can be determined according to not only the screen brightness but also the shutter speed, aperture value, sensitivity, and other shooting conditions. Further, by setting this threshold value to a value different from the threshold value set in S303 in FIG. 3, the determination process may have a hysteresis characteristic. In S2204, the luminance difference amount obtained in S2202 is compared with the threshold set in S2203. If the luminance difference amount after the filtering process is equal to or smaller than the threshold value, the process advances to step S2205, and it is determined that the shooting scene has not been changed by the user and is not in an unstable state. As a return value, FALSE return processing is performed, and a series of processing ends. On the other hand, if the luminance difference amount after the filtering process is larger than the threshold value, the process proceeds to S2206, and it is determined that the user has changed the shooting scene and is in an unstable state. As a return value, TRUE return processing is performed and a series of processing ends.
The image data to be used may be data of a specific area within the shooting screen (for example, an area that occupies 80% of the screen), or when a subject area is specified within the shooting screen, a luminance difference with respect to the subject area. A quantity may be calculated. By comparing this with a set threshold value, the state of the photographic scene can be determined based on the luminance difference amount of the predetermined area.

Next, the photographing process of S213 shown in FIG. 2 will be described. The following process is executed.
(A1) AE processing for main exposure.
(A2) AF processing for main exposure.
(A3) SW1 and SW2 state determination processing.
(A4) Main exposure process.

The state determination process in (A3) is as follows.
The system control unit 112 determines the state of the photographing switch SW2 (ON / OFF). If the SW2 is in the ON state, the system control unit 112 proceeds to the main exposure process in (A4). If SW2 is in the OFF state, the state of the SW1 is determined. .
If the SW1 state is ON, the process returns to the SW2 state determination process again. However, if SW1 is OFF, the process ends without performing the main exposure process.

FIG. 22 is a flowchart for explaining an example of the main exposure AF process. First, in S2401, it is determined whether or not the main subject detection flag is TRUE. If TRUE, the process proceeds to S2402, and if FALSE, the process proceeds to S2403.
In S2402, the first setting is performed as the AF frame setting for main exposure (indicated by the numeral 1 in the round frame in FIG. 22), and in S2403, the second setting is set as the AF frame setting for main exposure (FIG. 22). In FIG. 22, the number 2 is shown in a round frame). The frame number setting here is different from the N × N frame set in the main subject region determination. In the present embodiment, in order to reduce the calculation amount of the AF evaluation value, a natural variable n satisfying “N> n” is used to set the frame to n × n. Further, in order to improve the S / N ratio, the frame size of N × N is described as “Size _N ”, and the frame size of n × n is described as “Size _n ”, so that “Size _N <Size _n ”. It is desirable to set the frame size to satisfy the above.

Further, the frame setting may be determined based on the detection result of the main subject. When the main subject has been detected, in order to reduce the calculation amount of the AF evaluation value and improve the S / N ratio, in S2402, an AF frame setting that satisfies “N> n, Size _N <Size _n ” (the first frame) Setting). If the main subject has not been detected, a fine subject is photographed in the frame set for main subject detection, and a phenomenon such as background loss may occur. Therefore, in order to increase the resolution of main subject detection, in S2403, AF frame setting (second setting) that satisfies “ν> N, Size _N > Size _ν ” is set. Here, ν is a natural number variable.

  Proceeding from S2402 to S2404, it is determined whether or not the degree of focus calculated in S2105 of FIG. 19 is “high”. If the in-focus degree is “high”, the process proceeds to S2405; otherwise, the process proceeds to S2406. In S2405, a first scan range (shown with a numeral 1 in a round frame in FIG. 22) is set around the current position of the focus lens 103. In this case, it is determined that the focus lens is positioned almost in focus by the continuous AF operation, that is, near the in-focus position where the focus evaluation value shows a peak, and processing for setting a narrow scan range is performed. .

  S2406 is a process for determining whether or not the degree of focus calculated in S2105 of FIG. 19 is “medium”. If the degree of focus is “medium”, the process proceeds to S2407; otherwise, the process proceeds to S2408. In S2407, a second scan range (shown with a numeral 2 in a round frame in FIG. 22) is set around the current position of the focus lens 103. Here, the focus lens is located near the in-focus position by the continuous AF operation, but it is determined that the in-focus degree is not as high as the “high” state, and a range wider than the first scan range is set. Is done. In S2408, it is determined whether or not the current position of the focus lens 103 is within the macro area. If the position is within the macro area, the process proceeds to S2409; otherwise, the process proceeds to S2410. In S2409, a third scan range (shown with a numeral 3 in a round frame in FIG. 22) corresponding to a macro area that has been stored in advance is set. In S2410, a fourth scan range (shown with a numeral 4 in a round frame in FIG. 22), which is the entire range stored in advance, is set. After S2405, S2407, S2409, and S2410, an AF scan for main exposure is performed in S2411. In S2412, after the focus lens 103 moves to the peak position calculated in the process described later, the return process is performed.

The flow of processing in the main exposure AF scan in S2411 is as follows.
(B1) Lens movement to the scan start position The focus lens 103 moves to the scan start position. Here, the “scan start position” is the end position of the scan range set in S2405, S2407, S2409, or S2410 in FIG.
(B2) Focus Evaluation Value Acquisition Processing The analog video signal read from the image sensor 106 is converted into a digital signal by the A / D conversion unit 107, and the image processing unit 108 extracts a high-frequency component of the luminance signal from the output. . The system control unit 112 stores this in the memory as focus evaluation value data.
(B3) Lens Position Acquisition Processing The current position of the focus lens 103 is acquired, and the system control unit 112 stores the position data in the memory.
(B4) Comparison processing between lens position and scan end position The system control unit 112 compares the current position of the focus lens 103 with the scan end position to check whether or not the two positions are equal. If both positions are equal, the process proceeds to the next (B5). If the two positions are different, the focus lens 103 moves by a predetermined amount in the scan end direction in accordance with a command from the system control unit 112, and then the process returns to (B2).
(B5) Peak Position Calculation Processing The peak position of the focus evaluation value is calculated from the focus evaluation value stored in (B2) and its lens position. Here, in calculating the peak position of the focus evaluation value, when a plurality of AF frames are set, the calculation can be performed based on the closest peak position of the main subject area determined by the main subject area determination described with reference to FIG. it can. Or you may employ | adopt another judgment method and may perform peak position calculation.

Next, the flow of the main exposure process will be described. The following process is executed.
(C1) Exposure of the image sensor 106 (C2) Data read processing Data corresponding to the electric charge accumulated in the image sensor 106 is read.
(C3) A / D Conversion Processing The A / D conversion unit 107 converts an analog signal read from the image sensor 106 into a digital signal.
(C4) Image Processing The image processing unit 108 performs various types of image processing on the digital signal output from the A / D conversion unit 107.
(C5) Image Compression Processing The image data processed in the above (C4) is compressed by the format conversion unit 109 according to a format such as JPEG under the control of the system control unit 112.
(C6) Data Transfer / Recording Process The data compressed in (C5) above is sent to the image recording unit 111 and recorded on a recording medium.

  As described above, in this embodiment, after the shooting scene changes, the subject area to be focused in the shooting screen is determined, and the focus is adjusted before shooting preparation. Thus, even when the shooting scene changes, the main subject can be quickly focused after the shooting preparation instruction. In addition, when the shooting scene is not confirmed, it is possible to prevent the focus adjustment operation from being performed frequently by stopping the lens drive for focus adjustment, and to reduce power consumption without impairing the appearance of the screen. Can do.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

DESCRIPTION OF SYMBOLS 101 Shooting lens 102 Aperture and shutter 103 Focus lens 105 AF processing part 106 Image pick-up element 108 Image processing part 112 System control part 121 Moving body detection part

Claims (7)

An imaging device that performs focus adjustment by obtaining a focus signal indicating a focused state based on image data obtained by imaging a subject with an imaging device,
Instruction means for instructing shooting preparation;
Focus adjustment means for performing a focus adjustment operation based on the focus signal;
Determination means for determining the state of the shooting scene,
The focusing means is
Before the shooting preparation instruction, a first focus adjustment operation for calculating the focus signal in a predetermined scan range to specify a subject area to be focused and adjusting the focus, and sequentially acquiring the focus signal And a second focus adjustment operation for adjusting the focus to the higher side,
After the shooting preparation instruction, perform the focus adjustment by calculating the focus signal in the scan range based on the specified subject area to be focused,
An imaging apparatus that performs the first focus adjustment operation when a change in a shooting scene is detected by the determination unit during the second focus adjustment operation before the shooting preparation instruction .   The determination means calculates a temporal difference amount related to luminance in the shooting screen using the image data, and determines the stability of the shooting scene by comparing the difference amount with a threshold value. The imaging device according to claim 1.   The imaging apparatus according to claim 1, wherein the determination unit extracts a feature amount of a subject image by performing a filtering process on the difference amount.   The imaging apparatus according to claim 2, wherein the determination unit changes the threshold value according to a shutter speed, an aperture value, or sensitivity.   5. The imaging apparatus according to claim 1, wherein the determination unit determines a subject area to be focused in a shooting screen when the shooting scene changes.   The determination unit specifies the subject area based on the image data, calculates the difference amount for the subject area, and determines the state of the shooting scene based on the threshold and the calculated difference amount of the subject area. The imaging apparatus according to claim 5, wherein the imaging device is determined. A focus control method for an image pickup apparatus that performs focus adjustment by obtaining a focus signal indicating a focus state based on image data obtained by imaging a subject with an image pickup device,
An instruction step for instructing shooting preparation;
A determination step for determining the state of the shooting scene;
Before the shooting preparation instruction, a first focus adjustment operation for calculating the focus signal in a predetermined scan range to specify a subject area to be focused and adjusting the focus, and sequentially acquiring the focus signal And a second focus adjustment operation for adjusting the focus to the higher side,
A focus adjustment step of performing focus adjustment by calculating the focus signal in a scan range based on the specified subject area to be focused after the shooting preparation instruction , and
In the focus adjustment step, the first focus adjustment operation is performed when a change in the shooting scene is detected in the determination step during the second focus adjustment operation before the shooting preparation instruction. A focusing control method for the imaging apparatus.

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